[11.11] A Comparison of Three Methods of Photographic Plate Photometry

We have investigated the accuracy of three methods of
photographic plate photometry for stars: (1) eye estimates,
(2) measurement of the plates with an iris microphotometer;
and (3) digitizing the plate image with the aid of a Kodak
DCS200 CCD camera and processing the image file with the
NOAO's IRAF software. Thirteen standard stars in the open
cluster M25 were measured, using each of the three methods,
on seven typical plates from the Maria Mitchell Observatory
collection. Plotting the measured, ``instrumental''
magnitudes of the stars against their standard magnitudes
allowed us to determine the accuracy (rms deviations) of
each method in the same units of standard stellar
magnitudes. All the eye and microphotometer measurements
were done independently by two of the authors (F.T. and
C.S.). Somewhat surprisingly, eye estimates were found to
be, on average, more precise than the two other,
``objective'' methods. However, the differences are not
large: for all three methods rms deviations lie in the range
0.1 - 0.2 magnitudes, eye estimates being closer to the
lower value and microphotometer measurements to the upper
value of this range. Thus, accuracy should not be a decisive
criterion in the choice between these methods. We discuss
other criteria that would be more useful in choosing a
method --- speed, the available field of view, accessibility
of the required hardware.

The author(s) of this abstract have provided an email address
for comments about the abstract:
vladimir@mmo.org